The present invention relates to objectively determining in real time the color of bulk material undergoing heat treatment, such as during roasting, to ensure an accurate, readily replicable end point for the process.
A variety of bulk materials, typically but not limited to food products such as nuts, kernels, beans, grains and the like, are subjected to heat treatment, i.e. roasting, to alter characteristics of the materials, such as taste, aroma, hardness, color, moisture content and the like. Roasting must be carried on until the desired characteristic(s) have been attained, but must then be quickly terminated to prevent an over-roasting and a resulting deterioration of the product. Determining the roasting end point, however, is difficult when dealing with bulk material that is in motion, e.g. being stirred or tumbled.
One of the most widely roasted food products is coffee, and for simplicity the remainder of this application will primarily address the roasting of coffee beans. Those skilled in the art will recognize, however, that the present invention is equally applicable to other food products as well as non-food bulk materials that may require heat treatment.
At the present, and practically for as long as coffee has been consumed, green coffee beans are roasted in a hot environment, e.g. a flow of hot air, of the appropriate temperature, for example in the vicinity of about 700.degree. F. As roasting progresses, moisture in the beans is first evaporated, volatiles are driven off, and the beans begin to change color while oils accumulate on the surface of the beams. The roasting of coffee beans is supervised by a roastmaster, who monitors the progress of the roast and, based on experience, terminates it when he judges the beans to have the "right color". The determination of what the color of the coffee beans should be to attain optimal taste and aroma, and what it actually is during the roasting process, is done subjectively by the roastmaster.
As a result, there will almost invariably be differences in the extent to which beans are roasted, both from one batch to the next, even though they are supervised by the same roastmaster, and how different roastmasters determine the end point for the roasting process. Further, each locality where coffee beans are roasted requires its own roastmaster.
This limits the market for a given roasting plant and therewith its size since roasted coffee, and particularly premium coffee, has a limited shelf life which prevents it from being shipped over long distances, warehousing and the like. Thus, multiple, geographically dispersed, relatively small roasting plants are common in today's coffee industry. Uniform quality, however, is difficult to attain because the determination of the roasting process depends on the subjective judgment and decisions of different roastmasters at the plants.
The uniformity of roasting would be greatly enhanced if the roasting end point could be objectively determined. It is generally agreed that the color of the roasted product, e.g. coffee beans, is the best indicator when roasting should end. Instruments, such as spectrometers and reflectometers, are well known and can be used for objectively establishing the color of objects. However, such instruments are difficult to use in bulk processes because the individual particles of the bulk, e.g. the coffee beans, are in constant motion.
For example, to measure the color of coffee beans with a reflectometer it was thought necessary to position an individual coffee bean immediately in front of the reflectometer to prevent differences in the distance between any given bean and the reflectometer from resulting in inaccurate readings. Selecting individual beans and analyzing their color, however, is impractical because it is time consuming and the remainder of the beans continue to be roasted so that, by the time the color of the bean in question has been established, the color of the remaining beans, and therewith their aroma, may have already changed.
Because of these difficulties, the roasting of coffee beans (and other food products) has not changed much over time. Relatively small batches are roasted, one at a time, and a roastmaster subjectively determines when roasting should end. Thus, the coffee roasting industry continues to be a fragmented industry of many small operators characterized by a lack of uniformity in the way the beans are roasted and their ultimate aroma is established.